Luciferases are enzymes commonly used as reporters when analyzing molecular events in cells. When used as a reporter, the amount of luciferase in a cell can be indicative of a particular cellular event or condition. As such, many assays have been developed for measuring the amount of luciferase contained in biological samples. These assays typically involve assessing the amount of luciferase present in the sample by measuring the amount of luciferase enzymatic activity, and luciferase enzymatic activity is reflected by the destruction of luciferase enzymatic substrate or creation of a corresponding reaction product. Luciferases can react with a suitable substrate to produce light as one of the reaction products. The amount of light of this luminescent reaction can be measured, and used to determine the presence or amount of luciferase in a sample.
Luciferases that use coelenterazine as a substrate to produce luminescence include Renilla, Gaussia, Metridia and Obelia. These luciferases catalyse the oxidation of coelenterazine to yield coelenteramide, CO2 and light. This reaction is shown below:
It is well known that coelenterazine can be oxidized and produce light in the absence of luciferase. Luminescence produced in this way is called autoluminescence. This autoluminescence creates a background signal and thus reduces the sensitivity of luciferase detection assays. In particular, coelenterazine autoluminescence reduces the ability to detect small amount of luciferase, such as when the autoluminescence signal is of similar magnitude to the luminescent signal generated by the luciferase.
Unwanted coelenterazine autoluminescence may be increased by certain assay components, including components of the sample to be tested and desired assay components, such as detergents and proteins. Non-ionic detergents, for example, are often used as cell lysis agents to solubilize luciferase and make substrate accessible, while proteins are typically present in samples to be tested (e.g. cells, cell culture media supplemented with serum). Thus, under many desirable assay conditions, autoluminescence of coelenterazine can reduce sensitivity of luciferase assays.